Plasma etching method

ABSTRACT

A plasma etching method and apparatus are provided in which a distance between an ejection opening (20a) in a plasma generator (2) for ejecting an active species gas and a surface of an object to be etched can be changed to thereby shorten the time required for a surface flattening operation and reduce the cost of equipment as well. To this end, the ejection opening (20a) of a predetermined diameter is disposed in confrontation with a desired convex of the object to be etched in the form of a wafer (110). The active species gas in the form of an F gas (G) is ejected from the ejection opening (20a) to the convex to thereby flatten it through etching. A distance between the ejection opening and the convex is changed by means of a Z drive mechanism (4) to provide an etching area corresponding to an area of the convex, thus performing effective flattening of the wafer (110).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a plasm etching method and apparatusfor locally etching convex portions on a surface of an object to betreated.

2. Description of the Related Art

For a surface etching technology for etching a surface of an object suchas a silicon wafer, there have been proposed a variety of techniques inwhich an object to be etched is exposed to a plasma-excited activespecies gas atmosphere so as to grind and polish the entire surface ofthe object, or in which an object to be etched is partially masked witha non-masked portion thereof being etched by means of an active speciesgas to form a circuit pattern.

In recent years, in place of the technique of etching the entire surfaceof an object, new technologies such as a TTV (Total Thickness Variation)technique, an LTV (Local Thickness Variation) technique and the likehave been proposed in which convexes on a surface of an object to beetched such as a silicon wafer, a silicon-on-insulator device (SOI) andthe like are subjected to localized etching, to thereby thin the etchedobject, or flatten the surface to improve variations in shaping orconfiguration of the object (for example, see Japanese Patent Laid-OpenNo. 6-5571).

FIG. 14 schematically shows the principle of such conventionaltechniques. In this figure, a reference numeral 100 designates a plasmagenerator which generates a plasma gas containing an active species gasG which is injected to a surface of an object to be etched in the formof a wafer 110 by means of a nozzle 101 through its opening 102.

The wafer 110 is disposed on and fixed to a stage 120 so that the stage120 can be moved in horizontal directions to guide a convex portion 111of the wafer 110 into a position just under the opening 102 of thenozzle 101. Then, the active species gas G is ejected to the convexportion 111 of the wafer 110 to locally etching the convex portion 111to thereby flatten the surface of the wafer 110.

In the above-mentioned conventional techniques, however, there arise thefollowing problems. The sizes or dimensions of respective convexes ofthe convex portion 111 are varying, that is, for example with a siliconwafer having a diameter of 8 inches, there is a first one having anangle-shaped configuration with a highest or thickest near-centerportion and a lower peripheral portion, a second one having acone-shaped bottom configuration with a highest or thickest peripheralportion and a lowest or thinnest central portion, a third one having amultitude of small convexes and concaves each having a diameter of lessthan several millimeters, and a fourth one of mixed type having a mixedconfiguration with at least two of the above types being superposed ormixed with each other. In this manner, the convexes on the surface ofthe wafer are not uniform in size or dimensions thereof and not of thesingle type, but varying in size and type thereof.

On the other hand, since the active species gas is ejected from thenozzle 101, the diameter D of the opening 102 of the nozzle 101 issubstantially the same as the diameter of an area to be etched of thewafer 110, so that the area of the wafer 110 is uniformly etched bymeans of the active species gas G. Accordingly, in the case where thewafer 110 has a multitude of convexes 111 of varying diameters on asurface thereof, the diameter D of the nozzle opening 102 has to be setso as to meet the diameter of the smallest one of the convexes, as shownin FIG. 15. This is because if the diameter D of the nozzle opening 102is set to a value corresponding to that of a larger convex 111b,concaves 112 near and around small convexes 111a are to be etched whenetching the small convexes 111a. However, with the technique in whichthe diameter D of the nozzle opening 102 is matched to that of thesmallest convex 111a, upon etching a larger convex 111b, a number of(i.e., from several to tens) etching treatments are required, thusprolonging the time necessary for one surface flattening operation.

For this reason, in order to carry out such a surface flatteningoperation in a short period of time using the above-mentionedconventional technique, it is generally required that a plurality (e.g.,two in the illustrated example) of plasma generators 100-1, 100-2 havingdifferent diameters of nozzle openings be provided for respectivetreatment chambers A, B so as to etch the wafer 110 by means of theplasma generators 100-1, 100-2 in sequence. For example, the treatmentchamber A is constructed such that it is equipped with the plasmagenerator 100-1 having a nozzle 101 with its opening of 30 mm, and thetreatment chamber B is constructed such that it is equipped with theplasma generator 100-2 having a nozzle 101 with its opening of 7 mm. Awafer 110 is first supplied to the treatment chamber A in whichrelatively large convexes 111b on a surface of the wafer 110 each havinga diameter equal to or greater than 30 mm are subjected to plasmaetching. The wafer 110 thus treated is then transported to the treatmentchamber B in which convexes 111 a each having a diameter less than 30 mmare plasma etched.

With such a technique, however, the surface flattening time is in factshortened, but at least two treatment chambers A, B equipped with theplasma generators 100-1, 100-2 are required, resulting in a substantialincrease in the cost of equipment. Moreover, the wafer 110 has to betransported from the treatment chamber A to the treatment chamber B,thus prolonging the time of the entire etching treatments required.

SUMMARY OF THE INVENTION

In view of the above, the present invention is intended to provide anovel and improved plasma etching method and apparatus in which adistance between an ejection opening in a plasma generator for ejectingan active species gas and a surface of an object to be etched can bechanged to thereby shorten the time required for a surface flatteningoperation and reduce the cost of equipment as well.

In order to achieve the above object, according to one aspect of thepresent invention, there is provided a plasma etching method comprisingthe steps of:

disposing an ejection opening of a predetermined diameter in plasmagenerating means in confrontation with a prescribed convex of an objectto be etched; and

ejecting an active species gas from the ejection opening to the convexto thereby flatten it through etching;

wherein a distance between the ejection opening and the convex ischanged to provide an etching area corresponding to an area of saidconvex.

With the above method, the active species gas is ejected from theejection opening of the predetermined diameter in the plasma generatingmeans toward the convex, whereby the convex is etched and flattened.

In the case of the convex being large, the distance between the ejectionopening and the convex is increased, whereas in the case of the convexbeing small, the distance is decreased, so that there is ensured anetching area corresponding to the varying size or area of the convex,whether large or small, thus flattening the convex in an effectivemanner.

In a preferred form of the plasma etching method of the invention, aperiod of time of ejecting the active species gas is controlled inaccordance with the area of the convex. Thus, the ejection time of theactive species gas can be increased so as to flatten the convex having alarge area in a reliable manner. On the other hand, the ejection time ofthe active species gas can be shortened so as to flatten the convexhaving a small area in a reliable and effective manner.

In a further preferred form of the plasma etching method of theinvention, a density of the active species gas is controlled inaccordance with the area of the convex. Thus, the density of the activespecies gas can be increased so as to flatten the convex having a largearea in a reliable and effective manner. On the other hand, the densityof the active species gas can be shortened so as to flatten the convexhaving a small area in a reliable and effective manner.

In a still further preferred form of the plasma etching method of theinvention, a hydrogen gas is supplied to surroundings of the activespecies gas ejected from the ejection opening. Thus, the active speciesgas spreading outside the convex reacts with hydrogen, therebypreventing those portions of the object to be etched other than theconvex from being etched unnecessarily.

According to another aspect of the present invention, there is provideda plasma etching apparatus comprising:

plasma generating means having an ejection opening of a predetermineddiameter for ejecting an active species gas excited by a plasma;

distance changing means for changing a distance between the ejectionopening of the plasma generating means and a convex of an object to beetched, the object being disposed in confrontation with the ejectionopening; and

first control means for controlling a distance-changing operation of thedistance changing means in accordance with an area of the convex.

With the above construction, if the convex of the object to be etchedconfronting with the ejection opening of the plasma generating means islarge, the first control means controls the distance changing means soas to increase the distance between the ejection opening and the convex,so that the active species gas from the ejection opening can diffuse ina wide area to spread over the entire surface of the convex to therebyflatten the large convex. On the other hand, if the convex is small, thedistance between the ejection opening and the convex is decreased, sothat diffusion of the active species gas becomes limited, allowing theactive species gas to reach the small convex alone.

In a preferred form of the plasma etching apparatus of the invention,second control means is provided for controlling a period of time ofejecting the active species gas in accordance with the area of theconvex. Thus, the second control means serves to increase the ejectiontime of the active species gas for a large convex, and decrease it for asmall convex.

In a further preferred form of the plasma etching apparatus of theinvention, third control means is provided for controlling a density ofthe active species gas in accordance with the area of the convex. Thus,the third control means serves to increase the density of the activespecies gas for a large convex, and decrease it for a small convex.

In a still further preferred form of the plasma etching apparatus of theinvention, a hydrogen gas is supplied to surroundings of the activespecies gas ejected from the ejection opening.

The above and other objects, features and advantages of the presentinvention will more readily be understood by those skilled in the artfrom the following detailed description of the invention when taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a plasma etching apparatus inaccordance with a first embodiment of the present invention;

FIG. 2 is a block diagram of a controller;

FIG. 3 is a schematic view showing a record to be stored in a recordingmedium, in which FIG. 3(a) shows the position and size of a convex, andFIG. 3(b) shows the stored state of the record;

FIG. 4 is a flow chart showing the control operation of the controller;

FIG. 5 is a schematic side elevational view showing a relationshipbetween a first and a second set value representative of the respectiveheights of ejection openings and a reference value representative of anetching area;

FIG. 6 is a schematic plan view showing swinging movements of the convexportions;

FIG. 7 is a schematic side elevational view showing an example of asilicon wafer;

FIGS. 8(a)-8(d) is a schematic view showing the operation of the plasmaetching apparatus of FIG. 1;

FIG. 9 is a flow chart showing a flow of control of the controller ofthe plasma etching apparatus in accordance with a second embodiment ofthe present invention;

FIGS. 10(a)-10(d) is a schematic view showing the operation of theplasma etching apparatus of FIG. 9;

FIG. 11 is a view showing the construction of a plasma etching apparatusin accordance with a third embodiment of the present invention;

FIG. 12 is a flow chart showing the control operation of a controller ofthe plasma etching apparatus of FIG. 11;

FIG. 13 is a cross sectional view showing a modified form of a Z drivemechanism;

FIG. 14 is a schematic view showing the principle of a conventionalplasma etching apparatus;

FIG. 15 is a schematic view showing a surface flattening treatment inaccordance with the conventional plasma etching apparatus; and

FIG. 16 is a schematic view showing a construction of a conventionalplasma etching apparatus which is used for carrying out a surfaceflattening treatment in a short period of time.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, preferred embodiments of the present invention will be described indetail while referring to the accompanying drawings.

FIRST EMBODIMENT

FIG. 1 shows the construction of a plasma etching apparatus constructedin accordance with a first embodiment of the present invention.

The plasma etching apparatus as illustrated comprises a treatmentchamber in the form of a vacuum vessel 1, a plasma generator 2 installedon the vacuum vessel 1, an X-Y drive mechanism 3 disposed in the vacuumvessel 1, a distance varying means in the form of a Z drive mechanism 4disposed below the vacuum vessel 1, and a first and a second controlmeans in the form of a controller 5.

The plasma generator 2 comprises a conduit 20, a plurality of gascylinders 22-1, 22-2, 22-3 respectively storing gases to be supplied tothe conduit 20 through supply pipes 21, and a microwave oscillator 23mounted on an outer side of the conduit 20.

Specifically, the conduit 20 is fixed to an upper portion of the vacuumvessel 1 and has an ejection opening 20a of a predetermined innerdiameter D directed toward a stage 30.

The gas cylinders 22-1, 22-2, 22-3 store a sulfur hexafluoride (SF₆)gas, an oxygen (O₂) gas, and an argon (Ar) gas, respectively.

The microwave oscillator 23 comprises a magnetron and the like, andserves to radiate a microwave of a predetermined power toward a plasmagenerating area defined inside the conduit 20.

With the above arrangement, a mixed gas comprising the SF₆ gas, the O₂gas, and the Ar gas with a predetermined composition is supplied to theconduit 20, and microwave of the predetermined magnitude or power isradiated by the microwave oscillator 23 toward the plasma generatingarea in the conduit 20, so that a plasma containing an active speciesgas in the form of fluorine (F) gas G is created, the F gas beingflowing toward a downstream side. Thus, the conduit 20 ejects the F gasto a surface of an object to be etched in the form of a wafer 110,thereby etching it.

On the outside of the conduit 20, there is provided an exhaust pipe 24through which unnecessary etching products created upon F-gas etchingare caused to discharge to the outside of the vacuum vessel 1 under theaction of a vacuum pump 24a.

Outside the vacuum vessel 1, there is provided a gas cylinder 22-4storing therein a hydrogen gas which is to be supplied to the vacuumvessel 1 to make the interior space of the vacuum vessel 1 into ahydrogen atmosphere.

The X-Y drive mechanism 3 is a well-known mechanism which is capable ofmoving the stage 30 in an X-axis direction and in a Y-axis direction(i.e., in the right and left direction and in a direction perpendicularto the drawing sheet of FIG. 1) by means of unillustrated servo-motors.

The Z drive mechanism 4 is also a well-known conveying mechanism formoving the X-Y drive mechanism 3 in a Z-axis direction (i.e., in avertical direction in FIG. 1) so as to change the distance between theejection opening 20a of the conduit 20 and the adjacent surface of thewafer 110. Actually, the Z drive mechanism 4 comprises a linear guidedevice 40 and an electric motor 42.

More specifically, the linear guide device 40 is fixed to a support 41firmly attached to a lower surface of the vacuum vessel 1, and has ashaft 40a which is coupled at its upper end to the X-Y drive mechanism3. The motor 42 is controlled by the controller 5 and has a rotationshaft 42a coupled to the linear guide device 40.

With this arrangement, when the motor 42 is energized to rotate itsrotation shaft 42a in one direction, the linear guide device 40 coupledto the rotation shaft 42a converts the rotary motion of the rotationshaft 42a into an upward movement of its shaft 40a. At this time, theshaft 40a, the upper end of which is coupled to the X-Y drive mechanism3, raises the X-Y drive mechanism 3, whereby the stage 30 is moved in anupward direction together with the X-Y drive mechanism 3, casing thewafer 110 to approach the ejection opening 20a. On the other hand,reverse rotation of the rotation shaft 42a of the motor 42 causes thestage 30 to fall or lower, thus moving the wafer 110 away from theejection opening 20a.

In this regard, if there is created dust during vertical movements ofthe shaft 40a of the linear guide device 40, it is discharged to theoutside by means of a dust pump 10 mounted on the vacuum vessel 1.

The controller 5 serves to control the X-Y drive mechanism 3 and the Zdrive mechanism 4. As illustrated in FIG. 2, the controller 5 comprisesa CPU 50, a driver 51 connected to the CPU 50 through a bus, a ROM 52and a RAM 53, and is connected to the X-Y drive mechanism 3 and the Zdrive mechanism 4 through an interface 54, which is indicated at areference symbol IF in FIG. 2.

The driver 51 is a drive mechanism capable of reproducing data stored inthe recording medium 55 such as a floppy disc, a magneto-optical disc,etc. The recording medium 55 used for the driver 51 pre-stores datarelating to respective convexes existing on the surface of the wafer110.

FIG. 3 is a schematic view showing the convex data stored in therecording medium 55. As shown in this figure, let us assume that thereare N convexes on the surface of the wafer 110, and that position datarepresentative of the position of each convex and area-and-height datarepresentative of the area and height of each convex are measured andstored in the recording medium 55 beforehand. More specifically, asclearly shown in FIG. 3(a), for a nth (n≦N) convex 111, a position dataPn representative of the position of the nth convex 111 in X-Ycoordinates, an area data Ln representative of the diameter of thenearest contour to a reference line B1 indicated at a chain line, and aheight data Hn representative of the height of the nth convex 111 in a Zcoordinate are recorded or stored as a single piece of record. As shownin FIG. 3(b), such record data for the 1st through Nth convexes 111 arestored in the recording medium 55.

The CPU 50 has a function of generating an X-Y control signal C1 forcontrolling the X-Y drive mechanism 3 and a Z control signal C2 forcontrolling the Z drive mechanism 4 based on the data read out of therecording medium 55 through the RAM 53 and outputting it to the X-Ydrive mechanism 3 and the Z drive mechanism 4.

A control program to be executed by the CPU 50 for performing such afunction is stored in the ROM 52, so that the CPU 50 can carry outvarious control based on the control program.

FIG. 4 is a flow chart showing a control operation of the controller 5.As illustrated in FIG. 4, the controller 5 controls the X-Y drivemechanism 3 and the Z drive mechanism 4, and sequentially processes the1st through Nth convexes 111 in this order. Specifically, the CPU 50reads out the position data Pn from the record for the nth convex 111(steps S1, S2), and generates an X-Y control signal C1 for controllingthe X-Y drive mechanism 3 at a high speed so that the nth convex 111 ismoved to a position just under the ejection opening 20a, as shown inFIG. 1 (step S3).

Subsequently, the area data Ln for the nth convex 111 is read in and Itis determined whether the area data Ln is greater than a predeterminedreference value L0 (step S4).

When the area data Ln is greater than the reference value L0, thecontroller 5 generates a Z control signal C2 for controlling the Z drivemechanism 4 so that the distance between the ejection opening 20a andthe reference surface B1 is adjusted to a first predetermined value Z0("YES" in step S4, and step S5). On the other hand, if the area data Lnis not greater than the first predetermined value, a Z control signal C2is generated for controlling the Z drive mechanism 4 such that thedistance between the ejection opening 20a and the reference surface B1is adjusted to a second predetermined value Z0', which is less than thefirst predetermined value Z0 ("NO" in step S4, and step S11).

In this regard, it is to be noted that the reference value L0 is a valueof the diameter of a diffusion area of the F gas G when the height ofthe ejection opening 20a from the reference surface B1 is of the firstpredetermined value Z0, and hence it represents a corresponding etchingarea. Similarly, the reference value L0' is a value of the diameter of adiffusion area of the F gas G when the height of the ejection opening20a from the reference surface B1 is equal to the second predeterminedvalue Z0', and hence it represents a corresponding etching area. Thesereference values are experimentally determined beforehand.

As seen from FIG. 4, the controller 5 reads in the height data Hn,calculates a stay time Tn substantially in proportion to the height dataHn, and controls such that the nth convex 111 is stayed stationary at aposition just under the ejection opening 20a only for the stay time Tn(steps S6, S7). That is, the controller 5 performs substantially thesame processing as it controls an ejection time of the F gas G ejectedfrom the ejection opening 20a in accordance with the size of the convex111.

In this case, however, when the ejection opening 20a is at a height ofthe first predetermined value Z0, the diameter of the correspondingetching area is equal to the reference value L0. Thus, as shown in FIG.6, if the area Ln of the nth convex 111 is greater than the referencevalue L0, a large part of the peripheral portion of the nth convex 111might remain intact (non-etched) after the etching treatment.

In order to cope with this problem, the controller 5 generates, afterthe lapse of the stay time Tn, an X-Y signal C1 for swingingly movingthe nth convex 111 by a length of L (=(Ln-L0)/2) both in the X-axisdirection and in the Y-axis direction (step S8).

Similarly, when the ejection opening 20a is at a height of the secondpredetermined value Z0', the controller 5 generates an X-Y controlsignal C1 for moving the nth convex 111 by a distance L (=(Ln-L0')) bothin the X direction and in the Y direction.

Thereafter, as illustrated in FIG. 4, it is determined whether the nthconvex 111 is the last one (step S9). If the answer to this question isnegative, the next position data Pn+1 for the next (n+1)th convex 111 isread in so that the X-Y drive mechanism 3 is fast controlled to swiftlymove the next convex 111 to a position just under the ejection opening20a. Then, the same processing as above is repeated ("NO" in step S9,steps S10, S2 and S3). On the other hand, if the nth convex 111 is thelast one, the processing is finished ("YES" in step S9).

Now, the operation of the plasma etching apparatus according to thisembodiment will be described, which realizes a plasma etching methodaccording to the present invention. Here, for a better understanding ofthe invention, a process of flattening a silicon wafer 110 having fourconvexes 111-1 through 111-4 will be described.

First, let us assume that upon measuring the silicon wafer 110, therecords of the respective convexes 111-1 through 111-4 be (P1, L1, H1).(P2, L2, H2), (P3, L3, H3) and (P4, L4, H4), respectively, and that thefollowing conditions be established:

L1>L0, L2=L0, L0>L3>the reference value L0', L4=L0'

The recording medium 55 storing the above records is set on the driver51 of the controller 5, as shown in FIG. 2, and the plasma generator 2and the controller 5 shown in FIG. 1 are actuated so that the F gas G isejected from the ejection opening 20a of the diameter D toward thesilicon wafer 110. Simultaneous with this, the CPU 50 reads in theposition data P1 from the record for the convex 111-1 (steps S1, S2 inFIG. 4), and generates an X-Y control signal C1 to the X-Y drivemechanism 3.

Thus, based on the position data P1, the X-Y drive mechanism 3 drivesthe stage 30 at a high speed to place the convex 111-1 to a positionjust under the ejection opening 20a (step S3 in FIG. 4). At this moment,an area data L1 for the convex 111-1 is read in, but the area data L1thus read in is greater than the reference value L0, so that a Z controlsignal C2 is output from the controller 5 to the Z drive mechanism 4which drives the X-Y drive mechanism 3 and the stage 30 to move inunison in a downward direction to such an extent that the distancebetween the ejection opening 20a and the reference surface B1 becomesequal to the first predetermined value Z0 ("YES" in step S4, and step S5in FIG. 4).

As a consequence, an etching area of the reference value L0 is ensured,so that the convex 111-1 is etched by the F gas G ejected to anddiffused over this etching area.

At this time, the convex 111-1 stays at a position just under theejection opening 20a only for the period of time T1 calculated based onthe height data H1 (step S7 in FIG. 4), so that the F gas G is ejectedto the convex 111-1 for a longer period of time. As a result, theetching area for the convex 111-1 is flattened very well. Since the areadata L1 of the convex 111-1 is greater than the reference value L0, anX-Y control signal C1 is generated from the controller 5 to the X-Ydrive mechanism 3, whereby the convex 111-1 is swung or moved by adistance (L1-L0)/2 both in the X-axis direction and in the Y-axisdirection, thus etching the peripheral portion of the convex 111-1 in auniform manner (step S8 in FIG. 4), whereupon the F gas G diffuses tothe outside of the convex 111-1, giving rise to a possibility thatportions other than the convex 111-1 might be etched. However, theatmosphere surrounding the F gas G is filled with a hydrogen gassupplied from the gas cylinder 22-4, so the F gas G having diffused tothe outside of the convex 111-1 reacts with the hydrogen gas to beturned into an inactive HF gas. As a result, substantially no etchingwill take place on the portions of the wafer 110 outside the convex111-1.

Thereafter, the next convex 111-2 is selected as a target, and theposition data P2 for the convex 111-2 is read in ("NO" in steps S9, S10and S2 in FIG. 4), whereby the convex 111-2 is moved to a position justunder the ejection opening 20a at a high speed (step S3 in FIG. 4), asshown in FIG. 8(b). Thereafter, the same processing operation as in thecase of the convex 111-1 will be carried out (steps S4 through S9). Inthis connection, however, it is to be noted that since H2<H1, the staytime T2 of the convex 111-2 is shorter than the stay time T1 of theconvex 111-1. Also, due to the fact that the area data L2 of the convex111-2 is equal to the reference value L0, a relation {(L2-L0)/2=0} isestablished, resulting in no swinging movement of the convex 111-2 inthe X-axis and Y-axis directions.

After the processing of the convex 111-2, the convex 111-3 is selectedas the following target, and the position data P3 of the convex 111-3 isread in, so that the convex 111-3 is fast moved to a position just underthe ejection opening 20a ("NO" in steps S9, S10, S2, S3 in FIG. 4).Subsequently, the area data L3 of the convex 111-3 is read in, which isless than the reference value L0, so that the stage 30 is driven to movein the upward direction to such an extent that the distance between theejection opening 20a and the reference surface B1 is reduced to thesecond preset value Z0' ("NO" in steps S4 and S11 in FIG. 4).

As a consequence, a limited etching area of the reference value L0' isensured, the convex 111-3 is subjected to etching by means of the F gasG which is ejected to and diffused over that etching area.

After this, substantially the same processing operation is carried outas in the case of the convex 111-1. Thus, the convex 111-3 is stayedstationary just under the ejection opening 20a only for a period of timeT3 (<T2) calculated on the basis of the height data H3 (steps S6 and S7in FIG. 4), and then it is swung or moved by a distance (L3-L0')/2 bothin the X-axis direction and in the Y-axis direction, so that the convex111-3 is uniformly etched (step S8 in FIG. 4).

Then, the convex 111-4 is selected as a target, and the position data P4thereof is read in. As shown in FIG. 8(d), the convex 111-4 is moved toa position just under the ejection opening 20a at a high speed ("NO" insteps S9, S10, S2, and S3). Thereafter, the same processing operation iscarried out as in the case of the above-mentioned convex 111-3 (stepsS4, and S11 through S8). Here, it is to be noted that the stay time T4of the convex 111-4 is the shortest, and since the area data L4 of theconvex 1114 is equal to the reference value L0', there is no swingingmovement of the convex 111-4 in the X-axis and Y-axis directions.

In this manner, the entire processing operations of the silicon wafer110 have been finished ("YES" in step S9 in FIG. 4).

With the plasma etching apparatus as described above, a plurality ofsilicon wafers 110 each having a diameter of 6 inches were processedwith the result that the total thickness variation (TTV) thereof wasimproved from 0.48 μm by 0.25 μm on the average, and the standarddeviation of variation thereof is equal to or less than 0.03. Thus, itwas found that the plasma etching apparatus of the present inventionexhibits satisfactory performance as a wafer flattening apparatus.

As clearly seen from the foregoing, according to this embodiment, for aconvex 111 on a surface of the wafer 110 which has an area data Lngreater than the predetermined reference value L0, the stage 30 isdriven to move in the downward direction to make the distance betweenthe ejection opening 20a and the convex 111 larger so as to ensure acorrespondingly large etching area, whereas for a convex 111 having anarea data Ln equal to or less than the predetermined reference value L0,the stage 30 is driven to move in the upward direction to make thedistance between the ejection opening 20a and the convex 111 smaller soas to ensure a smaller etching area corresponding to the small convex111. With this arrangement, by the use of a single plasma generator 2with an ejection opening 20a having a predetermined diameter D, it ispossible to flatten a variety of convexes 111 of varying areas ordiameters, as a result of which provision of a single treatment chamberis satisfactory, thereby reducing the cost of equipment. Moreover, astep or process of repeatedly transporting a wafer 110 from onetreatment chamber to another for a plurality of treatments orprocessings can be omitted, so the total throughput of the apparatus canbe improved to a substantial extent.

Furthermore, the stay time Tn of each convex is controlled by the heightthereof, so that a period of time of ejecting an F gas G can be ensuredcorresponding to the convex height. As a consequence, a variety ofconvexes 111 having various sizes or areas can be flattened in areliable and effective manner.

Since the F gas being ejected is surrounded by a hydrogen atmosphere, itis possible to etch the convexes 111 exclusively with high reliability.

SECOND EMBODIMENT

A plasma etching apparatus in accordance with a second embodiment of thepresent invention will next be described below, which is different fromthe aforementioned plasma etching apparatus in accordance with the firstembodiment in that the distance between the ejection opening 20a and awafer 110 to be processed can be varied in a continuous manner.

FIG. 9 is a flow chart showing the control operation of the controller 5of this embodiment. As shown in FIG. 9, the steps S1 through S8 forsequentially processing the 1st through Nth convexes 111 in this order,and the steps S2, S3 of reading in the position data Pn of the nthconvex 111 and moving this convex 111 to a position just under theejection opening 20a are the same as the corresponding steps of theabove-mentioned first embodiment.

However, as shown in step S4, the control operation of this embodimentdiffers from the first embodiment in that the distance Zn between theejection opening 20a and the reference surface B1 of the wafer 110 (seeFIG. 3(a)) is controlled in accordance with the area data Ln.

More specifically, the controller 5 calculates the distance Zn using thefollowing equation based on the area data Ln of the nth convex 111,

Zn=k×Ln (k: a proportionality factor) and generates a Z control signalC2 for driving the Z drive mechanism 4 to move in the vertical directionso that the actual distance between the ejection opening 20a and thereference surface B1 becomes equal to the thus calculated distance valueZn.

Here, it is to be noted that the value Zn is such a value that when theF gas G is ejected from this height, an etching area to be etched by theF gas G has a diameter substantially equal to the area data Ln of thenth convex 111, which is dependent on the proportionality factor kexperimentally determined.

The nth convex 111 being in the above-mentioned state is stayedstationary just under the ejection opening 20a only for a period of timeTn substantially proportional to the height data Hn, during which it issubjected to an etching operation. After completion of such processingof the nth convex 111, processing moves to the following or (n+1)th one111 ("NO" in steps S5 through S7, steps S8 and S2).

With the above arrangement, for example, in the case of a silicon waferbeing flattened as illustrated in FIG. 7, the respective distances Z1through Z4 between the reference surface B1 and the ejection opening 20awith the 1st through 4th convexes 111-1 through 111-4, respectively, arecontinuously varied in accordance with the sizes or areas of theseconvexes 111-1 through 111-4, so that the F gas G can be ejected to anddiffused over all the convexes 111-1 through 111-4.

Accordingly, swinging movements of the convexes 111-1 through 111-4 asshown in step S8 in FIG. 4 can be omitted, thus making it possible tocorrespondingly shorten the period of time of the etching operation.

The construction and operation of this embodiment other than the aboveare substantially similar to those of the aforementioned firstembodiment, and hence a description thereof is omitted.

THIRD EMBODIMENT

A plasma etching apparatus in accordance with a third embodiment of thepresent invention will now be described below, which is different fromthe aforementioned plasma etching apparatuses in accordance with thefirst and second embodiments in that the density of F gas G can bevaried in dependence upon the size or area of each convex 111.

FIG. 11 illustrates the construction of the plasma etching apparatus ofthis embodiment, and FIG. 12 is a flow chart showing the controloperation of the controller 5 of this embodiment.

As shown in FIG. 11, the plasma etching apparatus of this embodiment isequipped with a third control means in the form of an ejection densitycontroller 6 for controlling the operations of electromagnetic valves25-1 through 25-3 provided on the gas cylinders 22-1 through 22-3 and amicrowave oscillator 23.

In the course of the control operation of the controller 5, asillustrated in FIG. 12, the steps S1 through S11 for sequentiallyprocessing the 1st through Nth convexes 111 in this order, and the stepsS3 through S5 and step S12 of reading in the position data Pn of the nthconvex 111 and moving this convex 111 to a position just under theejection opening 20a and controlling the distance Z between the ejectionopening 20a and the reference surface B1 based on the area data Ln arethe same as the corresponding steps of the above-mentioned firstembodiment.

However, as shown in steps S6 and S7, the control operation of thisembodiment differs from the first embodiment in that the ejectiondensity of the F gas G from the conduit 20 is controlled in accordancewith the height data Hn of the nth convex 111. Specifically, thecontroller 5 calculates the ejection density pn using the followingequation based on the height data Hn of the nth convex 111;

ρn=m×Hn (m: a proportionality factor) and generates a density controlsignal C3 to the ejection density controller 6 for controlling theactual ejection density of the F gas G from the ejection opening 20a tothe thus calculated ejection density ρn. Here, it is to be noted thatthe value ρn is such a value that when the F gas G of the density ρn isejected to the nth convex 111, it is possible to flatten the nth convex111 in a predetermined short period of time T0. The value ρn isdependent on the proportionality factor m which is determinedexperimentally.

The density control signal C3 indicates an amount of the F gas Gcomprising SF₆, O₂ and Ar with a predetermined composition, and anoscillation frequency of the microwave oscillator 23. These values forthe F gas amount and the oscillation frequency are beforehandexperimentally collected as data.

The controller 5 outputs the density control signal C3 to the ejectioncontroller 6, and performs, after the lapse of the predetermined timeT0, control of swingingly moving the nth convex 111 both in the X-axisand Y-axis directions, after which processing is moved to the following(n+1)th convex 111 (steps S8 through S11, and step S2).

On the other hand, the ejection density controller 6 shown in FIG. 11generates a control signal C4 based on the density control signal C3from the controller 5 to thereby control the electromagnetic valves 25-1through 25-3, and it also generates a control signal C5 to therebycontrol the microwave oscillator 23.

Specifically, the electromagnetic valves 25-1 through 25-3 arecontrolled to open and close by the ejection density controller 6, sothat the SF₆ gas, the O₂ gas and the Ar gas in the gas cylinders 22-1,22-2 and 22-3 are supplied to the conduit 20 at respective quantitiesindicated by the density control signal C3, and the microwave oscillator23 is controlled to radiate microwave into the conduit 20 at anoscillation frequency indicated by the density control signal C3.

With the above arrangement, for example, in the case of a silicon waferbeing flattened as illustrated in FIG. 7, the ejection density ρ1 of theF gas G for the convex 111-1 is the greatest, and the ejection densitiesρ2, ρ3 for the convexes 111-2, 111-3 decrease in this order, with theejection density ρ4 for the convex 111-4 being the smallest.Accordingly, it is possible to flatten the convexes 111-1 through 111-4in a predetermined short period of time T0 in a reliable manner, so incomparison with the aforementioned first embodiment in which the staytime of a convex increases in dependence on the size or area thereof,the time required for etching is extremely shortened.

The construction and operation of this embodiment other than the aboveare substantially similar to those of the aforementioned first andsecond embodiments, and hence a description thereof is omitted.

It should be understood that the present invention is not limited to theabove-described embodiments but can be modified or changed in a varietyof ways within the scope and spirit of the present invention as definedin the appended claims.

For example, although in the above-mentioned embodiments, it isconstructed such that the stage 30 is moved vertically to change thedistance between the ejection opening 20a and the wafer 110, the stage30 can be stationary with the conduit 20 of the plasma generator 2 beingmoved toward or away from the wafer 110.

Moreover, during the operation of the plasma etching apparatus, the Fgas G is continuously ejected from the conduit 20, but during the timewhen processing is transferred from one convex to the following convex,ejection of the F gas G may be stopped.

Furthermore, although the plasma generating means comprises a plasmagenerator 2 which radiates microwave of a predetermined power toward theplasma generating area in the conduit 20 to thereby generate a plasmacontaining an active species gas in the form of an F gas G, it cancomprise, in place of the plasma generator 2, an inductively coupledplasma generator (ICP) using a high-frequency wave, a capacitivelycoupled plasma generator, a plasma generator using a helicon wave, anelectron cyclotron resonance (ECR) source, or the like, for example.

Further, the plasma generating gas comprises a mixed gas containing SF₆,O₂ and Ar, but SF₆ in the mixed gas may be replaced by afluorocarbon-based gas such as CF₄.

Still more, although in the control of the controller 5 in the thirdembodiment, height control is effected at two stages or in a stepwisemanner in steps S4, S5 and S12 of FIG. 12 as in the first embodiment, itcan be carried out in a continuous manner as in the control of thesecond embodiment (step S4 in FIG. 9).

In the above-mentioned embodiments, the distance adjusting meanscomprises the Z drive mechanism 4 which is constructed of the linearguide device 40 and the motor 42, but as shown in FIG. 13, it caninstead comprise a Z drive mechanism 4' which is constructed of a rotaryguide device 40', a motor 42, and a rotation shaft 42a of a gearmechanism 43. That is, the rotational force of the rotation shaft 42a ofthe motor 42 is received by the rotary guide device 40', and therotation of the rotation shaft 40a' of the rotary guide device 40' isthen converted into a vertical movement by means of the gear mechanism43.

As described in detail in the foregoing, according to the presentinvention, it is possible to perform a surface flattening treatment onan object to be etched which has convexes having varying sizes or areassimply by changing the distance between a convex to be etched and anejection opening for ejecting an active species gas in an plasmagenerating means. This serves to shorten the time required for thesurface flattening operation. Such a surface flattening operation can becarried out by use of the single plasma generating means, so provisionof a single treatment chamber is satisfactory for treating or processinga variety of convexes of varying sizes or areas, resulting in asubstantial reduction in the cost of equipment. Also, a step or processof transporting the object to be etched from one treatment chamber toanother treatment chamber can be omitted, thus contributing to animprovement in the total throughput to a substantial extent.

Moreover, a period of time of ejecting the active species gas to aconvex can be controlled in accordance with the size or area of theconvex, so as to flatten the convex having a large area in a reliablemanner. On the other hand, the ejection time of the active species gascan be shortened so as to flatten the convex having a small area in areliable and effective manner.

Furthermore, a density of the active species gas can be controlled inaccordance with the area of the convex, so that the time required forthe surface flattening operation can further be reduced.

Still further, a hydrogen gas is supplied to surroundings of the activespecies gas ejected from the ejection opening, so that the activespecies gas spreading outside the convex reacts with hydrogen, therebypreventing unwanted etching of those portions of the object other thanthe convex. Thus, the surface flattening operation can be carried outwith high precision.

What is claimed is:
 1. A plasma etching method comprising the stepsof:disposing an ejection opening of a predetermined diameter in plasmagenerating means in confrontation with a prescribed convex of an objectto be etched; and ejecting an active species gas from said ejectionopening to said convex to thereby flatten it through etching; wherein adistance between said ejection opening and said convex is varied toprovide an etching area corresponding to an area of said convex.
 2. Theplasma etching method according to claim 1, wherein a period of time ofejecting said active species gas is controlled in accordance with thearea of said convex.
 3. The plasma etching method according to claim 1,wherein a density of said active species gas is controlled in accordancewith the area of said convex.
 4. The plasma etching method according toclaim 1, wherein a hydrogen gas is supplied to surroundings of saidactive species gas ejected from said ejection opening.